Deepest Known Volcanic Eruption Discovered – A Field of Glass Under The Sea

Almost on the cusp of the Mariana Trench, before it plunges down into the very bowels of the ocean, scientists have found something rare and wonderful. Sometime in 2015, an underwater volcano experienced a massive eruption, spewing molten magma into the surrounding ocean.

As the incredibly hot magma meets the water, it begins to rapidly cool. The result? A vast field of volcanic glass. And, even more spectacularly, at a depth of 4,050-4,450 metres (2.51 to 2.76 miles) it’s the deepest known volcanic eruption ever found on Earth.

This large field of volcanic glass stretches 7.3 kilometres (4.5 miles) along a region known as the Mariana Trough, a back-arc basin associated with the active volcanic arc that runs along the lip of the Mariana Trench.

Since this region sits right on the edge of a subduction zone, where the edge of one tectonic plate slips under another, volcanic activity is not unexpected, nor even uncommon. But studying this activity isn’t easy.

“We know that most of the world’s volcanic activity actually takes place in the ocean, but most of it goes undetected and unseen,” said marine geologist Bill Chadwick of Oregon State University and NOAA’s Pacific Marine Environmental Laboratory.

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“Undersea quakes associated with volcanism are usually small, and most of the instrumentation is far away on land. Many of these areas are deep and don’t leave any clues on the surface. That makes submarine eruptions very elusive. Undersea volcanoes can help inform us about how terrestrial volcanoes work and how they impact ocean chemistry, which can significantly affect local ecosystems,” Chadwick said.